How do collisions affect the ranging accuracy?

Hi, when you have many nodes trying to perform TWR in the same area, how do the collisions affect (theoretically/practically) their ranging performance?

Generally a collision will result in either a receive error or simply a failure to see anything. Assuming the firmware is written to cope with error conditions then these have the same end result, one or both of the range attempts will fail.
Normally any ranges received will still be good but the percentage of range attempts that succeed will drop significantly. How big the impact is depends on how many collisions you are getting.